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Syncronizing the PTO driveline
Most single u-joint drive shafts (vs. a double caradan-type) with a joint on each end are designed to run at about 2 degrees total each out-of-line with very slight or no vibration. At about 5 degrees total or 2.5 degrees each is when you start to see vibration.
The vibration is caused by the joints being out of phase, that is, like was mentioned above the yokes on the ends should form an X to cancel the effects and be in-phase. Out-of-phase is a condition where as the shaft turns the yoke it drives the u-joint at 1.5 RPM's times faster than the input speed through 90 degrees of rotation. The next 90 degrees it slows down by 1.5 times RPM, speeds up, and slows down resulting in vibration.
As an experiment, take a 1/4" or 3/8" ratchet socket universal with two extension shafts and rotate one shaft as the "input" with your fingers. Allow the other "output" shaft to make a sharp angle and observe/feel the output shaft--it will feel like it's jerky or speeding up and slowing down every 90 degrees. If you were to connect another unversal to the input shaft and rotate it, to a certain degree, the output shaft would be nearly vibration-free.
To cancel or reduce vibration, you can have a double cardan joint on one end (which is two u-joints housed in a cast housing) and a regular u-joint on the other end.
Short of that, you may want to consider using a "constant velocity" or "CV" joint that uses balls in a cage (used on front wheel drive cars) that deleivers vibration-free power. There are Ag applications for these type of shafts with CV joints but can be expsensive.
U-joints are not considered "constant velocity" by definition since they are by nature out of phase if not phased with another u-joint on the other end of the shaft.
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Syncronizing the PTO driveline
Pull the shaft apart and turn one end 90 degrees and stick it back together. Like this:
O---------------[
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Syncronizing the PTO driveline
Well, there was a chance I got my info wrong since it's been a few years since I've done hands-on. But along with wracking the noggin' and some cursory investigation on the Web, the results were, well... mixed. Some sites didn't address rotating the yokes 90 degrees; some did. I looked at my Dodge Ram driveshaft and the yokes were aligned--but that doesn't really mean much since having the driveshaft in near perfect alignment the driveline path is aligned straight through from the transfercase through to the axle. Having lifted four offroad Jeeps over the years 10-12" I stand by my earlier comments as having to out-of-phase or rotating the yokes 90 degrees to cancel vibration.
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